: This project will test the following hypothesis: spinal motoneurons have feedback synaptic connections to the locomotor CPG and are active participants in the generation of the locomotor rhythm. The current assumption in the literature is that motoneurons are output elements only with no feedback to the CPG. Recent evidence from the embryonic Xenopus spinal cord has challenged this assumption. Intracellular microelectrode recordings of membrane potential from motoneurons and locomotor CPG interneurons in the in vitro spinal cord preparation of the adult lamprey will be used to determine 1) whether cholinergic agents act upon spinal neurons and 2) whether motoneurons make synaptic contact upon other motoneurons and CPG interneurons. To determine whether motoneurons are active participants in locomotor rhythm generation, extracellular recordings of ventral root activity will be made in the in vitro spinal cord preparation induced to swimming activity with bath application of an excitatory amino acid (i.e., fictive swimming). These additional experiments will determine whether the fictive swimming pattern is altered by 3) cholinergic agents, 4) electrical stimulation of ventral roots, and 5) photo-ablation of motoneurons. Due to their large numbers and high activity levels, motoneurons could have a significant influence on locomotor rhythm generation. To fully understand the locomotor CPG and to properly interpret how the locomotor CPG is modulated and controlled, it is important to know whether or not motoneurons participate in the generation of the basic locomotor pattern.